1. Field of the Invention
The invention concerns a suspension system for the operator's platform of agricultural or industrial vehicles.
2. Description of the Related Art
On slow-moving vehicles such as agricultural tractors and the like, the operator's platform on which an operator's cab or a four-column roll-over structure may be mounted usually is not supported on springs, but is attached with bumpers or rubber mounts to the vehicle body. Due to their small spring deflection, these mounts provide isolation of structure-borne noise, but do not provide significant elastic support for the operator's platform. Low-frequency mechanical vibrations generated by operation over rough terrain can be transmitted right through them to the attachment point of the operator's seat, without any damping. To assure at least a certain degree of comfort for the operator, the vertical, horizontal, transverse and pitch vibrations typically are absorbed by spring-mounting the operator's seat.
For ergonomic reasons, the spring support of the operator's seat should not be too soft, since this would increase the spring deflections and lead to comparatively large relative motion between the operating controls and the operator. If this happened during shock loads, the operator might lose contact with the operating controls and adjusting levers mounted on the operator's platform. Unfortunately, these limitations on vibration isolation'lead to a spring support for the seat whose resonant frequency may lie in the range of natural frequencies of several internal human organs, which is perceived as being uncomfortable. The spring support of the seat also does not prevent transmission of vibrations through operating controls mounted on the operator's platform.
EP-B1-0 273 796 describes an elastic support for the cab of an agricultural tractor, in which MacPherson struts are provided to absorb vibrations between a stiff chassis on the one hand and transverse structures connected to the cab on the other. This elastic support permits pitch vibrations about the transverse axis that give the operator an impression of tumbling motion, which may impair his control of the vehicle. The known arrangement requires a multitude of Panhard rods to absorb horizontal forces and is relatively costly. Furthermore, tuning of the elastic supports is difficult.